1. Field of the Invention
This invention relates to an ophthalmologic instrument such as, for example, a photo slit lamp including an illumination optical system for illuminating an eye to be tested, an observation optical system for observing the eye to be tested, and photograph means for photographing the eye to be tested, and more particularly to an improvement on an ophthalmologic instrument including a proper exposure control means for the photograph means, and an indication mechanism for indicating a proper exposure position of photograph to an inspector or ophthalmologist.
2. Related Art of the Invention
There are generally known a fundus camera, photo slit lamp, photographing apparatus for examination microscope, etc., as an ophthalmologic apparatus for observing and photographing an eye to be tested. Especially, regarding a photo slit lamp, exposure conditions at the time when a photo is taken are decided according to personal impressions or experiences of an inspector or ophthalmologist, since the object for observation and photograph spreads in various tissues of an anterior eye portion such as, cornea, iris, crystalline lens, etc.
Japanese Patent Early Disclosure (Kokai Koho) No. 56(1981)-72841 (hereinafter referred to as "A") discloses a comparable device wherein the exposure conditions are automatically decided. There are also Japanese Patent Early Disclosure Nos. 55(1980)-78218 (hereinafter referred to as "B") and 58(1983)-136328 (hereinafter referred to as "C") which disclose a light volume measurement of a portion to be photographed as a prerequisite for deciding the exposure condition as well as indication means for indicating the measuring position to the inspecter or ophthalmologist.
According to the disclosure of A, photographing conditions such as film speed, predetermined coefficient according to a photograph object portion of an eye to be tested, photograph magnitude, illumination conditions, etc. are preliminarily programmed in advance for computing proper exposure conditions, and based on the computed results, light volume to be emitted from a flashing tube as a photograph light source is properly adjusted. According to the disclosure of B, the image of an eye to be tested is divided into a plurality of picture elements, and light receiving elements corresponding to each of the picture elements and selection means thereof are provided, and at the same time, in order to show an inspector or ophthalmologist which picture element is being measured in its light volume information, a plurality of light emitting elements individually corresponding to the light receiving elements are indicated on the observation image in superposed relation, and a proper exposure volume is decided based on light volume information of the picture element under measurement. Similarly, according to the disclosure of C, the apparatus includes a pair of light emitting-light receiving elements which are movable in a plane optically conjugate to an observation image of an eye to be tested, an index light is projected to a photograph portion of the eye to be tested, the index image is shown to the inspecter or ophthalmologist in its state superposed on the observation image, by moving the pair of light emitting-receiving elements, the inspecter or ophthalmologist is allowed to select a portion to be measured, the light volume of a portion where the index light is projected is measured, and based on the measured results, the portion where the index light is projected is determined to be an object portion for photographing.
The apparatus disclosed in A has the disadvantage that it is hardly put into practical use, since the range of photograph conditions for obtaining a satisfactory picture is very limited due to the arrangement that the exposure conditions are decided by a predetermined program. On the other hand, the apparatus disclosed in B has such an advantage that it includes means for measuring light volume information per every picture element. However, it also has the disadvantage that the plurality of light emitting elements and light receiving elements per every picture element are required to provide individual correlation, and photograph condition information input means such as film speed, illumination condition (width of slit, length of slit, illumination lamp output), etc. and picture element selection means are required to operate separately. The disadvantage which the apparatus disclosed in C has is in difficulty of its operation. That is, since an index light is projected to the portion to be photographed and the portion where the index light is projected is measured, when the eye to be tested is moved, the object portion to be photographed is inevitably moved. Accordingly, the index light is required to follow from time to time the movement of the object portion to be photographed, i.e., the portion to be measured and change the projecting position of the index light.